The present invention relates to a method and apparatus for treating webs of wrapping material for rod-shaped articles which constitute or form part of smokers' products. More particularly, the invention relates to a method and apparatus for applying adhesive to running webs of such wrapping material. Still more particularly, the invention relates to improvements in a method and apparatus for applying adhesive paste to running webs of cigarette paper, artificial cork or other suitable wrapping material prior to subdivision of such webs into discrete uniting bands. The uniting bands can be used to connect filter plugs of unit length or multiple unit length with one or more tobacco-containing rod-shaped articles, e.g., with plain cigarettes, cigars or cigarillos.
It is already known to apply adhesive to a moving web of wrapping material in such a way that, when the web is subdivided into discrete uniting bands of square or rectangular outline, all four edges of each uniting band are adjacent to strips of adhesive which has been applied to one side of the web. This is achieved by resorting to a paster wherein a rotary element draws adhesive from a tank and has peripheral grooves distributed in such a way that the grooves form a pattern corresponding to the desired pattern of adhesive strips at one side of the moving web. The leader of the web is severed at regular intervals by one or more cutters to yield a succession of uniting bands which are attached to successive groups of coaxial rod-shaped articles. The groups are thereupon rolled about their respective axes during travel through a gap whose width is less than the diameter of a group whereby the uniting bands are converted into tubes which sealingly connect the articles of the respective groups to each other. Such procedure is normally resorted to in the manufacture of filter cigarettes, cigars or cigarillos.
It has become customary to provide the wrappers of filter plugs of filter cigarettes or like rod-shaped smokers' products with one or more holes or perforations which admit atmospheric air into the column of hot tobacco smoke. The admission of atmospheric air is believed to be beneficial as regards the quantity of nicotine and/or condensates in the smoke which enters the smoker's mouth. Instead of using filter plugs with perforated wrappers, it is also possible and customary to resort to wrappers having a relatively high porosity so that one or more streamlets of cool atmospheric air can enter the tobacco smoke via pores rather than through artificially formed perforations of the wrapper for the filter plug.
Utilization of uniting bands which are provided with adhesive strips along their edges but not on the central portion of the adhesive-coated side is desirable and necessary in order to insure that the adhesive cannot clog the pores and/or artificially produced perforations, i.e., to insure the admission of predictable quantities of cool atmospheric air into the tobacco smoke. The aforementioned grooves in the periphery of the rotary adhesive-applying element of the paster insure that the central portion of a uniting band remains free of adhesive. The depth of all grooves is the same, i.e., the thickness of the strips which are applied to one side of the moving web and thereupon surround a centrally located uncoated area of each uniting band is the same. It is also known to drive the rotary element at a peripheral speed which exceeds or is less than the speed of lengthwise movement of the web in the region of the paster. This results in spreading of adhesive which forms the strips and in more uniform distribution of adhesive at one side of the web.
Problems arise in connection with the sealing of joints between the filter plugs and the plain cigarettes. More particularly, it can happen that the joints between the wrappers of two plain cigarettes and the two end portions of a tube which is obtained upon conversion of a uniting band as a result of rolling of a group consisting of two plain cigarettes and a filter plug of double unit length therebetween will produce leaks in regions where the end portions of the converted uniting band adhere to the wrappers of plain cigarettes. This results in admission of undesirable quantities of additional atmospheric air and is annoying to the smoker because the quantity of smoke which enters the mouth is less than anticipated. As a rule, the extent to which a converted uniting band (tube) surrounds the inner end portions of wrappers of plain cigarettes of unit length is in the range of a few millimeters. On the other hand, it is highly desirable that such regions be absolutely airtight, i.e., that atmospheric air be allowed to enter solely through the pores or perforations of a converted uniting band, namely, through pores or perforations in that portion of the converted uniting band which is not coated with adhesive. The establishment of pockets or clearances between the end portions of the converted (tubular) uniting band and the surrounded portions of wrappers of plain cigarettes which are connected to filter plugs is a problem which the manufacturers of filter cigarettes attempted to solve by applying thick strips of adhesive, i.e., by applying to the moving web adhesive in such quantities as to insure the establishment of a reliable circumferentially complete seal between each end portion of a converted uniting band and the adjacent portions of wrappers of plain cigarettes in a filter cigarette of double unit length.
The thickness of adhesive strips on the moving web of cigarette paper or the like cannot be increased at will for several reasons. First of all, the aforementioned spreading of adhesive as a result of slippage between the web and the rotary element of the paster is not predictable if the thickness of one or more adhesive strips is excessive. Secondly, the surplus of adhesive is likely to leak beyond the end portions of the converted uniting band and to contaminate the external surfaces of filter cigarettes. Still further, the surplus of adhesive causes the filter cigarettes to adhere to conveyors or other parts during further transport through a filter tipping machine. Also, the surplus of adhesive is likely to adhere to knives or cutters which are used to subdivide the moving web into discrete uniting bands and/or the knife or knives which are used to sever each filter cigarette of double unit length midway between its ends so that each such cigarette yields two coaxial filter cigarettes of unit length in a manner which is customary in presently known filter tipping machines. Finally, the surplus of adhesive can contaminate the surfaces flanking the aforementioned gap wherein the groups of coaxial rod-shaped articles are rolled to convert the uniting bands into tubes. Contamination of rolling means and/or knives entails lengthy interruptions of operation with attendant substantial losses to output, especially in a modern machine which turns out many thousands of smokers' products per minute.
Attempts to reduce the likelihood of contamination of filter tipping and analogous machines with adhesive paste include the application of relatively thick layers of adhesive only to those portions of uniting bands which adhere to the wrappers of plain cigarettes, cigars or cigarillos. This is satisfactory insofar as the prevention of development of pockets or the like is concerned; however, when the uniting bands are rolled to convert them into tubes which connect plain cigarettes or the like with filter plugs, the surplus of adhesive invariably emerges from within the convoluted uniting band and contaminates the wrapper(s) of the tobacco containing article(s). Therefore, the appearance of the final products is less than satisfactory and the squeezed out surplus of adhesive rapidly contaminates those components of the machine which roll the uniting bands as well as the parts which thereupon transport and/or otherwise manipulate the filter tipped products.